1. Field of the Invention
This invention relates generally to apparatus for transmitting and receiving signals and, more particularly, is directed to an apparatus for transmitting and receiving signals as found in a so-called cordless telephone.
2. Description of the Background
The standard telephone consists of a base unit and a handset unit connected to each other by an electrical cord. The base unit is connected by another cord to the telephone line network that is essentially worldwide. Although it is possible to speak with someone almost anyplace in the world it is necessary to stay within the electrical cord length of base unit. The simple fact that there is always a continuous physical connection between the person making the phone call and the fixed base unit can be a great inconvenience. This brought about the advent of the cordless telephone, which represents a significant improvement over the standard telephone.
In the cordless telephone, the handset and the base unit are not connected by a wire or cord but are connected only by radio waves. Thus, the only limitation on the movement between the base unit and the handset is the ability to maintain radio contact and, of course, applicable statutes and rules governing public communications.
Nevertheless, the cordless telephone also presents certain difficulties. In particular, there are a limited number of channels available for the radio communication between the handset and the base unit, therefore, if several cordless telephones are being used within the same general area there is a good chance that the signal transmitted from one handset unit to its own base unit may be picked up by the base unit of a neighboring cordless telephone, leading to crosstalk interference.
Accordingly, in such case, it is necessary to change the radio communication channel that was initially assigned to that particular cordless telephone. In order to change the communication channel established between the handset and the base unit, the operator has to change-over channel switches provided in both the handset and the base unit. Furthermore, because the handset and the base unit are usually distant from each other, it is very inconvenient and cumbersome to change the communication channel by operating the switches of the handset and the base unit of the cordless telephone system. In addition, even if the communication channel is changed, it is frequently the case that the communication link will still not be satisfactory, in which case it is necessary for the user to again change both the switches of the handset and the base unit at the same time.